Cutting insert, cutting tool, and method of manufacturing machined product

ABSTRACT

A cutting insert of an embodiment includes an upper surface including a first upper cutting edge and a second upper cutting edge, a lower surface including a first lower cutting edge and a second lower cutting edge, and a side surface. The side surface includes a first surface extending from the second upper cutting edge, a second surface extending from the first lower cutting edge, a third surface extending from the first upper cutting edge, and a fourth surface extending from the second lower cutting edge. The first surface and the fourth surface are parallel to a central axis. The second surface is inclined so as to depart from the central axis as going from the lower surface toward the upper surface. The third surface is inclined so as to depart from the central axis as going from the upper surface toward the lower surface.

TECHNICAL FIELD

The present embodiment relates to a cutting insert, a cutting tool, anda method of manufacturing a machined product.

BACKGROUND ART

As a cutting insert (hereinafter also referred to simply as “insert”)for use in a cutting process of workpieces, such as metals, a cuttinginsert described in Japanese Unexamined Patent Publication No.2010-523352 (Patent Document 1) is known. The insert described in PatentDocument 1 includes a major flank surface extending from a major cuttingedge close to an upper surface toward a minor cutting edge close to alower surface, and a minor flank surface extending from the minorcutting edge close to the upper surface toward the major cutting edgeclose to the lower surface. The major flank surface is inclined so as todepart from a central axis of a through hole as going from the uppersurface toward the lower surface. The minor flank surface is inclined soas to approach the central axis of the through hole as going from theupper surface toward the lower surface. The insert described in PatentDocument 1 is configured to be attached to a tool body (holder) by abolt (screw) to be inserted into the through hole. On this occasion, thetwo major flank surfaces on a side surface come into contact with thetool body.

When a cutting process is carried out using the insert described inPatent Document 1, a force is applied to the major cutting edge and theminor cutting edge used for cutting in a direction from the uppersurface toward the lower surface. Therefore, as a reaction against theforce, a force is apt to be applied to the two major flank surfacesbeing in contact with the tool body in the direction from the lowersurface toward the upper surface.

Here, the major flank surface is inclined so as to depart from thecentral axis of the through hole as going from the upper surface towardthe lower surface, thus making it easier for the insert to slide towarda workpiece. This makes it easier for the insert to slide laterally withrespect to the through hole configured to accept insertion of the bolt.Accordingly, the bolt can be subjected to a large lateral load, namely,a large shear stress. It can therefore be difficult to stably fix theinsert to the holder.

The present embodiment has been accomplished in view of the aboveproblem, and provides a cutting insert capable of being stably fixed tothe holder.

SUMMARY OF THE INVENTION

A cutting insert according to an embodiment includes an upper surfaceincluding a plurality of side parts, a lower surface including aplurality of side parts, a side surface located between the uppersurface and the lower surface, a plurality of upper cutting edges whichare individually located along one of the side parts on the uppersurface and individually include a first upper cutting edge and a secondupper cutting edge, and a plurality of lower cutting edges which areindividually located along one of the side parts on the lower surfaceand individually include a first lower cutting edge and a second lowercutting edge, and a through hole extending between the upper surface andthe lower surface. The first lower cutting edge is located below thesecond upper cutting edge. The second lower cutting edge is locatedbelow the first upper cutting edge. The side surface includes a firstsurface extending downward from the second upper cutting edge, a secondsurface extending upward from the first lower cutting edge, a thirdsurface extending downward from the first upper cutting edge, and afourth surface extending upward from the second lower cutting edge. Thefirst surface and the fourth surface are located along a central axis ofthe through hole. The second surface is inclined so as to further departfrom the central axis than the first surface as going from the lowersurface toward the upper surface. The third surface is inclined so as tofurther depart from the central axis than the fourth surface as goingfrom the upper surface toward the lower surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view that shows a cutting insert according to anembodiment of the present invention;

FIG. 2 is a top view of the cutting insert shown in FIG. 1;

FIG. 3 is a side view of the cutting insert shown in FIG. 2, taken alongA1 direction;

FIG. 4 is a side view of the cutting insert shown in FIG. 2, taken alongA2 direction;

FIG. 5 is a perspective view of the cutting insert shown in FIG. 1,taken from a lower surface side thereof;

FIG. 6 is a sectional view of section plane B1 of the cutting insertshown in FIG. 2;

FIG. 7 is a sectional view of section plane B2 of the cutting insertshown in FIG. 2;

FIG. 8 is a sectional view of section plane B3 of the cutting insertshown in FIG. 2;

FIG. 9 is a sectional view of section plane B4 of the cutting insertshown in FIG. 2;

FIG. 10 is a perspective view that shows a cutting tool according to anembodiment of the present invention;

FIG. 11 is an enlarged perspective view of a front end part in thecutting tool shown in FIG. 10;

FIG. 12 is a side view of the cutting tool shown in FIG. 10, taken froma front end side thereof along a rotation axis;

FIG. 13 is a schematic diagram that shows a step of a method ofmanufacturing a machined product according to an embodiment of thepresent invention;

FIG. 14 is a schematic diagram that shows a step of the method ofmanufacturing a machined product according to the embodiment of thepresent invention; and

FIG. 15 is a schematic diagram that shows a step of the method ofmanufacturing a machined product according to the embodiment of thepresent invention.

EMBODIMENTS FOR CARRYING OUT THE INVENTION <Cutting Insert>

A cutting insert 1 of an embodiment is described in detail below withreference to the drawings. For the sake of convenience, the drawingsreferred to in the following show, in simplified form, only maincomponents among components of the embodiment, which are necessary fordescribing the present invention. Therefore, the cutting insert of thepresent invention may include any optional component not shown in thedrawings referred to in the present description. Sizes of the componentsin the drawings are not faithful to sizes of actual components and tosize ratios of the actual components.

The cutting insert 1 (hereinafter also referred to simply as “insert 1”)of the embodiment includes an upper surface 3, a lower surface 5, a sidesurface 7, an upper cutting edge 9, a lower cutting edge 11, and athrough hole 13 as shown in FIGS. 1 to 9. As a material of the insert 1,for example, cemented carbide or cermet is usable.

As a composition of the cemented carbide, there are, for example, WC—Co,WC—TiC—Co, and WC—TiC—TaC—Co. The WC—Co is produced by adding cobalt(Co) powder to tungsten carbide (WC), followed by sintering. TheWC—TiC—Co is produced by adding titanium carbide (TiC) to WC—Co. TheWC—TiC—TaC—Co is produced by adding tantalum carbide (TaC) to WC—TiC—Co.

The cermet is a sintered composite material obtainable by compositingmetal into a ceramic ingredient. A specific example of the cermet is onewhich is composed mainly of a titanium compound, such as titaniumcarbide (TiC) or titanium nitride (TiN).

A surface of each of the above members constituting the insert 1 may becoated with a coating film by using chemical vapor deposition (CVD)method or physical vapor deposition (PVD) method. As a composition ofthe coating film, there are, for example, titanium carbide (TiC),titanium nitride (TiN), titanium carbonitride (TiCN), and alumina(Al₂O₃).

The upper surface 3 has a polygonal shape having rotational symmetry,and is formed into an approximately rectangular shape having rotationalsymmetry of 180° in the present embodiment as shown in FIG. 2. Therectangular-shaped upper surface 3 includes a plurality of upper cornerparts and a plurality of upper side parts located between the uppercorner parts adjacent to each other. Specifically, the upper surface 3includes four upper corner parts and two upper side parts correspondingto short sides of the rectangular shape in the present embodiment.

The lower surface 5 has a polygonal shape having rotational symmetrycorresponding to the upper surface 3. Similarly to the upper surface 3,the lower surface 5 is formed into an approximately rectangular shapehaving rotational symmetry of 180° in the present embodiment as shown inFIG. 5. The rectangular-shaped lower surface 5 includes a plurality oflower corner parts and a plurality of lower side parts located betweenthe lower corner parts adjacent to each other. Specifically, the lowersurface 5 includes four lower corner parts and two lower side partscorresponding to short sides of the rectangular shape in the presentembodiment.

The upper surface 3 and the lower surface 5 in the present embodimenthave the shape with rotational symmetry. In the case of having the shapewith rotational symmetry, the center of the rotational symmetrycorresponds to the center of the upper surface 3 or the center of thelower surface 5.

Although the lower surface 5 has the polygonal shape corresponding tothe upper surface 3 and has the same size, an entire outer edge of theupper surface 3 and an entire outer edge of the lower surface 5 are notlocated in an overlapped manner when seen through from above. The centerof the upper surface 3 and the center of the lower surface 5 are locatedin an overlapping manner, and the upper corner parts and the lowercorner parts are located in an overlapping manner, whereas the upperside parts and the lower side parts are not located in a completelyoverlapping manner when seen through from above.

Here, the polygonal shape does not denote a strict polygonal shape. Forexample, each of the upper corner parts on the upper surface 3 in thepresent embodiment is not made into a strict corner, but has a roundedshape in a top view. Each of the upper side parts on the upper surface 3in the present embodiment is not made into a strict straight line, butis made into a shape that protrudes outward in a top view.

The shapes of the upper surface 3 and the lower surface 5 are notlimited to the above embodiment. In the insert 1 of the presentembodiment, the upper surface 3 and the lower surface 5 have anapproximately square shape. Alternatively, the upper surface 3 and thelower surface 5 may have a polygonal shape, such as a triangular orhexagonal shape having rotational symmetry.

The insert 1 of the present embodiment includes the through hole 13extending between the upper surface 3 and the lower surface 5. Thethrough hole 13 is disposed for inserting a screw therethrough whenscrewing the insert 1 into the holder of a cutting tool.

In the insert 1 of the present embodiment, the through hole 13 islocated between the center of the upper surface 3 and the center of thelower surface 5. Therefore, a central axis O1 of the through hole 13extends vertically. In order to evaluate a position of each of thecomponents in the vertical direction in the insert 1 of the presentembodiment, a reference plane S that is orthogonal to the central axisO1 and located between the upper surface 3 and the lower surface 5 isset in the following.

The side surface 7 is located between the upper surface 3 and the lowersurface 5, and is connected to the upper surface 3 and the lower surface5. The side surface 7 includes a plurality of first surfaces 15, aplurality of second surfaces 17, a plurality of third surfaces 19 and aplurality of fourth surfaces 21.

The upper cutting edges 9 are respectively located along the upper sideparts on the upper surface 3. Each of the upper cutting edges 9 includesa first upper cutting edge 23 and a second upper cutting edge 25. Inother words, the insert 1 of the present embodiment includes two firstupper cutting edges 23 and two second upper cutting edges 25.

The first upper cutting edge 23 and the second upper cutting edge 25 arein the shape of a straight line, but are not located on a straight linein a top view. When the first upper cutting edge 23 and the second uppercutting edge 25 are in the shape of the straight line in the top view,it is avoidable that a cutting load is concentrated locally at the firstupper cutting edge 23 and the second upper cutting edge 25. It istherefore possible to enhance durability of the first upper cutting edge23 and the second upper cutting edge 25.

The first upper cutting edge 23 and the second upper cutting edge 25 arelocated so as to form an obtuse angle in a top view. Therefore, each ofthe upper side parts is in the shape that protrudes outward in the topview as described above. When the first upper cutting edge 23 and thesecond upper cutting edge 25 are so located, it is avoidable that acutting load is excessively concentrated at a boundary part between thefirst upper cutting edge 23 and the second upper cutting edge 25. It istherefore possible to suitably use the second upper cutting edge 25during a helical process or lapping process, while using the first uppercutting edge 23 as a major cutting edge, as described later.

The first upper cutting edge 23 is a segment used as the major cuttingedge during a cutting process of a workpiece. Upon attachment to theholder, the first upper cutting edge 23 is attached so as to depart fromthe workpiece as departing from the second upper cutting edge 25adjacent to the first upper cutting edge 23. The second upper cuttingedge 25 is a segment auxiliary used during the cutting process of theworkpiece, and is used during the helical process or lapping process.Upon attachment to the holder, the second upper cutting edge 25 isattached so as to depart from the workpiece as departing from the firstupper cutting edge 23 adjacent to the second upper cutting edge 25. Inother words, when the insert 1 is being attached to the holder, theboundary part between the first upper cutting edge 23 and the secondupper cutting edge 25 is located closest to the front end side of theholder.

When the upper cutting edge 9 being used is deteriorated due to thecutting process over a long period of time in the cutting tool using theinsert 1 of the present embodiment, the insert 1 needs to be temporarilyremoved from the holder and then reattached to the holder by turning theinsert 1 180° around the central axis O1. This makes it possible to usean unused other upper cutting edge 9 in the cutting process of theworkpiece.

Lower cutting edges 11 are respectively located on the lower side partson the lower surface 5. Each of the lower cutting edges 11 includes afirst lower cutting edge 27 and a second lower cutting edge 29. That is,the insert 1 of the present embodiment includes two first lower cuttingedges 27 and two second lower cutting edges 29.

The first lower cutting edge 27 and the second lower cutting edge 29 arein the shape of a straight line, but are not located on a straight linein a bottom view. When the first lower cutting edge 27 and the secondlower cutting edge 29 are in the shape of the straight line in thebottom view, it is avoidable that a cutting load is concentrated locallyat the first lower cutting edge 27 and the second lower cutting edge 29.It is therefore possible to enhance durability of the first lowercutting edge 27 and the second lower cutting edge 29.

The first lower cutting edge 27 and the second lower cutting edge 29 arelocated so as to form an obtuse angle in a bottom view. Therefore, eachof the lower side parts is in a shape that protrudes outward in thebottom view. When the first lower cutting edge 27 and the second lowercutting edge 29 are so located, it is avoidable that a cutting load isexcessively concentrated at a boundary part between the first lowercutting edge 27 and the second lower cutting edge 29. It is thereforepossible to suitably use the second lower cutting edge 29 during thehelical process or lapping process, while using the first lower cuttingedge 27 as the major cutting edge, as described later.

Similarly to the first upper cutting edge 23, the first lower cuttingedge 27 is a segment used as the major cutting edge during the cuttingprocess of the workpiece. Similarly to the second upper cutting edge 25,the second lower cutting edge 29 is a segment auxiliary used during thecutting process of the workpiece, and is used during the helical processor lapping process. When the lower cutting edge 11 being used isdeteriorated due to the cutting process over a long period of time inthe cutting tool using the insert 1 of the present embodiment, theinsert 1 needs to be temporarily removed from the holder and thenreattached to the holder by turning the insert 1 180° around the centralaxis O1.

The first lower cutting edge 27 is located below the second uppercutting edge 25 and the second lower cutting edge 29 is located belowthe first upper cutting edge 23 in a side view of the insert 1.Specifically, the segments of the cutting edges are located so as toensure overlapping between the first upper cutting edge 23 and the firstlower cutting edge 27 and overlapping between the second upper cuttingedge 25 and the second lower cutting edge 29 when the insert 1 is turnedupside down by reversing the central axis O1. Hence, the lower cuttingedge 11 is usable in the same manner as the upper cutting edge 9 byturning the insert 1 upside down.

A so-called honing process may be applied to a region in which the uppercutting edge 9 and the lower cutting edge 11 are located. That is,neither a ridge line along which the upper surface 3 and the sidesurface 7 intersect each other, nor a ridge line along which the lowersurface 5 and the side surface 7 intersect each other needs to be astrict line form formed by the intersection of the two surfaces. Theline-shaped ridge lines cause strength deterioration of the uppercutting edge 9 and the lower cutting edge 11. Therefore, round honing iscarried out to make the region into a curved surface shape.

A maximum width of the upper surface 3 in a top view of the insert 1 ofthe present embodiment is 6-25 mm. A height from the lower surface 5 tothe upper surface 3 is 1-10 mm. Here, the height from the lower surface5 to the upper surface 3 denotes a height in a direction parallel to thecentral axis O1 between an upper end of the upper surface 3 and a lowerend of the lower surface 5.

The side surface 7 includes the first surfaces 15, the second surfaces17, the third surfaces 19, and the fourth surfaces 21 as describedabove. The first surface 15 is a region of the side surface 7 whichextends downward from the second upper cutting edge 25. The secondsurface 17 is a region of the side surface 7 which extends upward fromthe first lower cutting edge 27. The third surface 19 is a region of theside surface 7 which extends downward from the first upper cutting edge23. The fourth surface 21 is a region of the side surface 7 whichextends upward from the second lower cutting edge 29.

As shown in FIG. 4, the first surface 15, the second surface 17, thethird surface 19 and the fourth surface 21 are sequentially located sideby side in a side view. In FIG. 4, the first surface 15 is locatedleftmost, and the second surface 17 is located on the right side of thefirst surface 15. The third surface 19 is located on the right side ofthe second surface 17, and the fourth surface 21 is located on the rightside of the third surface 19.

Each of the first surface 15, the second surface 17, the third surface19 and the fourth surface 21 in the present embodiment is a flatsurface. The first to fourth surfaces made up of the flat surfacesensures a stable fixing of the insert 1 to the holder when attaching theinsert 1 to the holder.

Thus in the present embodiment, the region of the side surface 7 locatedbetween the second upper cutting edge 25 and the first lower cuttingedge 27 is made up of the first surface 15 and the second surface 17,instead of a single flat surface region. The region located between thesecond lower cutting edge 29 and the first upper cutting edge 23 is alsomade up of the third surface 19 and the fourth surface 21, instead of asingle flat surface region.

The first surface 15 is located along the central axis O1 of the throughhole 13, and is parallel to the central axis O1 of the through hole 13in the present embodiment. The fourth surface 21 is located along thecentral axis O1 of the through hole 13, and is parallel to the centralaxis O1 of the through hole 13 in the present embodiment.

The second surface 17 is inclined so as to further depart from thecentral axis O1 than the first surface 15 as going from the lowersurface 5 toward the upper surface 3. Specifically, the second surface17 is inclined at an angle θ2 with respect to the central axis O1 in asectional view. A ridge line is formed between the first surface 15 andthe second surface 17 because the first surface 15 and the secondsurface 17 are located as described above. In FIGS. 7 and 8, a straightline L orthogonal to the reference plane S and parallel to the centralaxis O1 is indicated, the central axis O1 is replaced with the straightline L, and the angle θ2 is indicated by an inclination angle withrespect to the straight line L. The angle θ2 is settable to, forexample, approximately 1-10°.

The third surface 19 is inclined so as to further depart from thecentral axis O1 than the fourth surface 21 as going from the uppersurface 3 toward the lower surface 5. Specifically, the third surface 19is inclined at an angle θ1 with respect to the central axis O1 in asectional view. A ridge line is formed between the third surface 19 andthe fourth surface 21 because the third surface 19 and the fourthsurface 21 are located as described above. In FIGS. 8 and 9, a straightline L orthogonal to the reference plane S and parallel to the centralaxis O1 is indicated, the central axis O1 is replaced with the straightline L, and the angle θ1 is indicated by an inclination angle withrespect to the straight line L. The angle θ1 is settable to, forexample, approximately 1-10°. The angle θ1 is preferably identical tothe angle θ2.

As described above, the second surface 17 that is the region of the sidesurface 7 corresponding to the first lower cutting edge 27, and thethird surface 19 that is the region of the side surface 7 correspondingto the first upper cutting edge 23 are located so as to depart from thecentral axis O1 as departing from the cutting edge. The first lowercutting edge 27 and the first upper cutting edge 23 function as themajor cutting edge during the cutting process. The second surface 17 andthe third surface 19 are configured as described above, thereby makingit possible to enhance strength of the first lower cutting edge 27 andthe first upper cutting edge 23 which are subjected to a relativelylarge load.

The side surface 7 in the present embodiment also includes the firstsurface 15 corresponding to the second upper cutting edge 25, and thefourth surface 21 corresponding to the second lower cutting edge 29. Thefirst source 15 and the fourth source 21 are parallel to the centralaxis O1 in a sectional view, and are therefore orthogonal to thereference plane S. When the region of the side surface 7 which islocated between the second upper cutting edge 25 and the first lowercutting edge 27 is formed by a single surface region, it follows that onthe basis of the first lower cutting edge 27, the surface region departsfrom the central axis O1 as departing from the first lower cutting edge27. Inevitably on the basis of the second upper cutting edge 25, thesurface region approaches the central axis O1 as departing from thesecond upper cutting edge 25. This can degrade strength of the secondupper cutting edge 25.

Similarly, when the region of the side surface 7 which is locatedbetween the second lower cutting edge 29 and the first upper cuttingedge 23 is made up of a single surface region, it follows that on thebasis of the first upper cutting edge 23, the surface region departsfrom the central axis O1 as departing from the first upper cutting edge23. Inevitably on the basis of the second lower cutting edge 29, thesurface region approaches the central axis O1 as departing from thesecond lower cutting edge 29. This can degrade strength of the secondlower cutting edge 29.

However, the first surface 15 in the present embodiment has a surfaceconfiguration separately from the second surface 17 so that a ridge lineis formed therebetween. This makes it possible to enhance the strengthof the second upper cutting edge 25 while enhancing the strength of thefirst lower cutting edge 27. Similarly, the fourth surface 21 in thepresent embodiment has a surface configuration separately from the thirdsurface 19 so that a ridge line is formed therebetween. This makes itpossible to enhance the strength of the second lower cutting edge 29while enhancing the strength of the first upper cutting edge 23.

The second surface 17 is inclined so as to depart from the central axisO1 as going from the lower surface 5 toward the upper surface 3, whilethe third surface 19 is inclined so as to depart from the central axisO1 as going from the upper surface 3 toward the lower surface 5.Accordingly, a ridge line is also formed between the second surface 17and the third surface 19.

The insert 1 of the present embodiment includes the upper cutting edges9 and the lower cutting edges 11, and one of these cutting edge regionsis used during a cutting process. For example, when one of the uppercutting edges 9 is used during a cutting process, the rest of the uppercutting edges 9 is not used during the cutting process. A region of theside surface 7 corresponding to each of the upper cutting edges 9 notbeing used during the cutting process is used as a constraining surfaceagainst the holder configured to attach the insert 1 thereto.

During the cutting process, a force is applied to the upper cutting edge9 being used during the cutting process, in a direction from the uppersurface toward the lower surface. The insert 1 is fixed to the holder bya screw fitted into the through hole 13. Therefore, a force is apt to beapplied to the location of the upper cutting edge 9 not being usedduring the cutting process, in a direction from the lower surface towardthe upper surface.

On this occasion, when the region of the side surface 7 used as theconstraining surface is inclined so as to depart from the central axisO1 of the through hole 13 as going from the upper surface toward thelower surface, an excessively large load can be exerted on the screw.However, in the insert 1 of the present embodiment, the first surface 15and the fourth surface 21 are parallel to the central axis O1 in a crosssection including the central axis O1 of the through hole 13. This makesit possible for the holder to stably fix the insert 1 even on the firstsurface 15 and the fourth surface 21.

Also when another of the upper cutting edges 9 is used for a cuttingprocess, and when another of the lower cutting edges 11 is used for acutting process, the insert 1 is stably fixable on the first surface 15and the fourth surface 21 for the same reason.

Particularly in the insert 1 of the present embodiment, the firstsurface 15 and the fourth surface 21 are connected to the upper surface3 and the lower surface 5. It is therefore possible to increase an areaof each of the first surface 15 and the fourth surface 21, therebyensuring that the insert 1 is stably fixable on the first surface 15 andthe fourth surface 21.

To be specific, in the insert 1 of the present embodiment, the secondsurface 17 has a smaller width in the direction orthogonal to thecentral axis O1 as going from the lower surface 5 toward the uppersurface 3 in a side view. Similarly, the third surface 19 has a smallerwidth in the direction orthogonal to the central axis O1 as going fromthe upper surface 3 toward the lower surface 5 in a side view. Thismakes it possible to ensure a large area of each of the first surface 15and the fourth surface 21.

<Cutting Tool>

A cutting tool 101 of an embodiment of the present invention isdescribed below with reference to FIGS. 10 to 12. FIGS. 10 to 12 show astate in which the insert 1 is attached via a screw 107 to an insertpocket 105 of the holder 103. A chain double-dashed line in FIGS. 10 and11 indicates a rotation axis O2 of the cutting tool 101.

As shown in FIGS. 10 and 11, the cutting tool 101 of the presentembodiment includes the holder 103 having the rotation axis O2 andincluding a plurality of insert pockets 105 (hereinafter also referredto simply as “pockets 105”) on an outer peripheral surface on a frontend side of the holder 103, and the insert 1 to be attached to each ofthe pockets 105.

The holder 103 has an approximately columnar shape around the rotationaxis O2. The pockets 105 are disposed on the outer peripheral surface onthe front end side of the holder 103. The pockets 105 are portionsconfigured to attach the insert 1 thereto, and open into the outerperipheral surface and a front end surface of the holder 103. Thepockets 105 may be disposed at equal intervals or unequal intervals. Theholder 103 is provided with the pockets 105 and is therefore not in astrict columnar shape.

The inserts 1 are respectively attached to the pockets 105 disposed onthe holder 103. The inserts 1 are attached so that at least a part ofthe upper cutting edge or the lower cutting edge protrudes forwardbeyond the front end surface of the holder 103, namely, toward theworkpiece beyond the front end surface of the holder 103. Specifically,the inserts 1 in the present embodiment are attached to the holder 103so that a part of the first upper cutting edge and a part of the secondupper cutting edge protrude beyond the front end surface of the holder103.

Each of the inserts 1 is attached via the screw 107 to the pocket 105 inthe present embodiment. That is, each of the inserts 1 is attached tothe holder 103 by inserting the screw 107 into the through hole of theinsert 1, and then inserting a front end of the screw 107 into a screwhole (not shown) formed in the pocket 105, and thereafter fixing thescrew 107 into the screw hole. For example, steel and cast iron areusable as the holder 103. Of these materials, it is particularlypreferable to use high-rigidity steel.

<Method of Manufacturing Machined Product>

A method of manufacturing a machined product according to an embodimentof the present invention is described below with reference to FIGS. 13to 15. FIGS. 13 to 15 show the method of manufacturing the machinedproduct. The machined product is manufacturable by subjecting aworkpiece 201 to a cutting process. The manufacturing method in thepresent embodiment includes the following steps:

(1) rotating the cutting tool 101 as typified by the foregoingembodiment;

(2) bringing the upper cutting edge 9 or the lower cutting edge in thecutting tool 101 being rotated into contact with the workpiece 201; and

(3) moving the cutting tool 101 away from the workpiece 201.

More specifically, a first step is to bring the cutting tool 101relatively near the workpiece 201 while rotating the cutting tool 101around the rotation axis O2. A subsequent step is to cut the workpiece201 by bringing the upper cutting edge 9 as a cutting edge in thecutting tool 101 into contact with the workpiece 201 as shown in FIG.14. A final step is to keep the cutting tool 101 relatively away fromthe workpiece 201 as shown in FIG. 15.

In the present embodiment, the workpiece 201 is fixed and the cuttingtool 101 is brought near. In FIGS. 13 to 15, the workpiece 201 is fixedand the cutting tool 101 is rotated around the rotation axis O2. In FIG.15, the workpiece 201 is fixed and the cutting tool 101 is kept away.Although the workpiece 201 is fixed and the cutting tool 101 is moved ineach of the steps during the cutting process in the manufacturing methodof the present embodiment, it is, of course, not intended to limit tothis embodiment.

For example, in the step (1), the workpiece 201 may be brought near thecutting tool 101. Similarly, in the step (3), the workpiece 201 may bekept away from the cutting tool 101. When the cutting process iscontinued, it is necessary to repeat the step of bringing the uppercutting edge of the insert 1 into contact with different portions of theworkpiece 201, while the cutting tool 101 is kept rotating.

When the upper cutting edge being used is worn away, the upper cuttingedge not yet used needs to be used by rotating the insert 1 180 degreeswith respect to the central axis of the through hole. When all of theupper cutting edges are worn away, the lower cutting edge needs to beused by turning the insert up and down. Representative examples of thematerial of the workpiece 201 include carbon steel, alloy steel,stainless steel, cast iron, and nonferrous metals.

DESCRIPTION OF THE REFERENCE NUMERAL

-   1 cutting insert (insert)-   3 upper surface-   5 lower surface-   7 side surface-   9 upper cutting edge-   11 lower cutting edge-   13 through hole-   15 first surface-   17 second surface-   19 third surface-   21 fourth surface-   23 first upper cutting edge-   25 second upper cutting edge-   27 first lower cutting edge-   29 second lower cutting edge-   101 cutting tool-   103 holder-   105 insert pocket (pocket)-   107 screw-   201 workpiece

1. A cutting insert comprising: an upper surface comprising a first sidepart and a second side part; a lower surface comprising a third sidepart and a fourth side part; a first lateral surface located between thefirst side part and the third side part; a second lateral surfacelocated between the second side part and the fourth side part; an upperedge located at the first side part and comprising a first upper edgeand a second upper edge; and a lower edge being located at the thirdside part and comprising a first lower edge and a second lower edge,wherein a central axis is an imaginary line through a center of theupper surface and a center of the lower surface, the first lower edge islocated below the second upper edge and the second lower edge is locatedbelow the first upper edge, the first lateral surface comprises: a firstregion angled in a first direction relative to the central axis, and asecond region angled in a second direction relative to the central axis,the second direction is different from the first direction, and thesecond lateral surface comprises a flat region parallel to the centralaxis.
 2. The cutting insert according to claim 1, wherein the firstregion is separated from the third side part, and the second region isseparated from the first side part.
 3. The cutting insert according toclaim 1, wherein the lateral surface further comprises: a third regionangled relative to the first region, and a fourth region angled relativeto the second region, and the first region is located between the secondregion and the third region, the second region is located between thefirst region and the fourth region.
 4. The cutting insert according toclaim 3, wherein the third region and the fourth region are parallel tothe central axis.
 5. The cutting insert according to claim 3, whereinthe third region and the fourth region are connected to the uppersurface and the lower surface.
 6. The cutting insert according to claim3, wherein each of the first region, the second region, the third regionand the fourth region comprises a flat surface.
 7. The cutting insertaccording to claim 3, wherein the first region and the second region aredirectly adjacent to the third region and the fourth region.
 8. Acutting insert comprising: an upper surface comprising a first sidepart; a lower surface comprising a second side part; a lateral surfacelocated between the first side part and the third side part; an upperedge located at the first side part and comprising a first upper edgeand a second upper edge; and a lower edge being located at the secondside part and comprising a first lower edge and a second lower edge,wherein a central axis is an imaginary line through a center of theupper surface and a center of the lower surface, the first lower edge islocated below the second upper edge and the second lower edge is locatedbelow the first upper edge, the lateral surface comprises: a firstregion, a second region, a third region located between the first regionand the second region, and angled relative to the first region, and afourth region located between the third region and the second region,and angled relative to the second region, the third region is angled ina first direction relative to the central axis, the fourth region isangled in a second direction relative to the central axis, and thesecond direction is different from the first direction.
 9. The cuttinginsert according to claim 8, wherein the third region is separated fromthe second side part, and the fourth region is separated from the firstside part.
 10. The cutting insert according to claim 8, wherein thefirst region and the second region are parallel to the central axis. 11.The cutting insert according to claim 8, wherein the first region andthe second region are connected to the upper surface and the lowersurface.
 12. The cutting insert according to claim 8, wherein each ofthe first region, the second region, the third region and the fourthregion comprises a flat surface.
 13. The cutting insert according toclaim 8, wherein the third region and the fourth region are directlyadjacent to the first region and the second region.
 14. A cutting insertcomprising: an upper surface comprising a first side part; a lowersurface comprising a second side part; a lateral surface located betweenthe first side part and the third side part; an upper edge located atthe first side part and comprising a first upper edge and a second upperedge; and a lower edge being located at the second side part andcomprising a first lower edge and a second lower edge, wherein a centralaxis is an imaginary line through a center of the upper surface and acenter of the lower surface, the first lower edge is located below thesecond upper edge and the second lower edge is located below the firstupper edge, the lateral surface comprises: a first region angled in afirst direction relative to the central axis, and a second region angledin a second direction relative to the central axis, the second directionis different from the first direction, and an upper end of the secondregion is closer to the first side part than an upper end of the firstregion.
 15. The cutting insert according to claim 14, wherein the secondregion is separated from the second side part, and the first region isseparated from the first side part.
 16. The cutting insert according toclaim 14, wherein the lateral surface further comprises: a third regionangled relative to the first region, and a fourth region angled relativeto the second region, and the first region is located between the secondregion and the third region, the second region is located between thefirst region and the fourth region.
 17. The cutting insert according toclaim 16, wherein the third region and the fourth region are parallel tothe central axis.
 18. The cutting insert according to claim 16, whereinthe third region and the fourth region are connected to the uppersurface and the lower surface.
 19. The cutting insert according to claim16, wherein each of the first region, the second region, the thirdregion and the fourth region comprises a flat surface.
 20. The cuttinginsert according to claim 16, wherein the first region and the secondregion are directly adjacent to the third region and the fourth region.